Fluorine-containing elastomer compositions are used as materials of O-rings, gaskets, oil seals, diaphragms, hoses, rolls, seat members, etc. in various industrial fields such as automobile, ships, aircraft, hydraulic machines and general machine industries as well as environmental pollution-related fields. In particular, peroxide-curable fluorine-containing elastomers can be cured when fluororubbers have high fluorine concentrations, unlike the polyol curing or polyamine curing system. Furthermore, fluororubbers having iodine atoms at polymer chain ends have an advantage that they can be cured with peroxides without compounding metal oxides.
However, although peroxide-curable fluorine-containing elastomers have such good properties, they have low mold releasing properties and anticontamination of molds in the curing and molding steps. Thus, it is difficult to improve the working efficiency, and also the productivity tends to deteriorate due to the decrease of yields by cracking or breakage, when articles having complicated shapes are molded. Thus, external mold release. agents or internal mold release agents are used to improve the mold releasing properties of fluorine-containing elastomers. However, when internal mold release agents are used, a problem arises, that the physical properties of cured products deteriorate. When external mold release agents are used, the effect to improve the mold releasing properties decreases as the number of molding cycles increases. Therefore, it is necessary to repeatedly apply the external mold release agents to a mold, and further the commercial value of products may decrease since marks of the external release-agents remain on the surfaces of molded articles.
In the case of peroxide curing, burrs formed in the course of compression molding, in particular, parts of burrs which are in contact with an air, are not sufficiently cured, and thus stain the surfaces of molds or molded articles.
Various improvements have been proposed to solve the above problems of peroxide-curable fluorine-containing elastomer compositions, but they have their own drawbacks.
For example, fluorine-containing block polymers, which are disclosed in JP-A-59-40066 relating to a sealing material resistant to lubricant oils and JP-B-61-49327 relating to a fluorine-containing segmented polymer, contain 5 wt. % or more of non-elastomeric polymer chain segments, and thus they have drawbacks that properties greatly deteriorate when they are formulated in the form of fluororubber compositions and cured.
A non-tacky fluororubber composition, which is prepared by a method disclosed in JP-A-8-176388 comprising mixing a fluororubber and a fluorine-containing block polymer, can achieve effects to some extent. However, it has-a drawback that the content of a non-elastomeric component in the used fluororubbery thermoplastic elastomer is high, and thus it is not easy to mix the fluororubber and the fluorine-containing block polymer.